Interventional device recognition

ABSTRACT

The present invention relates to an apparatus (10) for tracking a position of an interventional device (11) respective an image plane (12) of an ultrasound field. The position includes an out-of-plane distance (Dop). A geometry-providing unit (GPU) includes a plurality of transducer-to-distal-end lengths (Ltde1 . . . n), each length corresponding to a predetermined distance (Ltde) between a distal end (17, 47) of an interventional device (11, 41) and an ultrasound detector (16, 46) attached to the interventional device, for each of a plurality of interventional device types (T1 . . . N). An image fusion unit (IFU) receives data indicative of the type (T) of the interventional device being tracked; and based on the type (T): selects from the geometry-providing unit (GPU), a corresponding transducer-to-distal-end length (Ltde); and indicates in a reconstructed ultrasound image (RUI) both the out-of-plane distance (Dop) and the transducer-to-distal-end length (Ltde) for the interventional device within the ultrasound field.

FIELD OF THE INVENTION

The present invention relates to the localization of an interventionaldevice using ultrasound. More specifically it relates to the recognitionof the type of interventional device that is attached to anultrasound-based localization system.

BACKGROUND OF THE INVENTION

Interventional devices such as needles, catheters and surgical tools areoften difficult to visualize in an ultrasound image due to the specularnature of their reflectivity, particularly at unfavorable incidenceangles.

In one solution to this problem, U.S. Pat. No. 4,249,539 describes anarrangement in which the tip of a medical needle includes an ultrasoundtransducer that is responsive to the ultrasound signals emitted by anultrasound imaging system. Upon detecting an ultrasound pulse from theultrasound imaging system, a circuit connected to the transducertriggers the insertion of the needle position into the ultrasound imagethrough either the generation of a return ultrasound pulse from theneedle tip, or through the simulation of such a return pulse using atime of flight delay.

In another solution to this problem, patent application WO2011138698describes a system for tracking an instrument in an ultrasound fieldwith an ultrasound receiver that is mounted to the instrument. The 3Dposition of the ultrasound receiver is obtained by beamforming thesignals received by it as the ultrasound beams of the ultrasound fieldsweep its field of view. The position of the ultrasound receiver is thendisplayed in the ultrasound image.

Document WO2015101949A1 discloses a tool navigation system employing anultrasound probe, an ultrasound scanner, an interventional tool, aplurality of ultrasound transducers, a tool tracker and an imagenavigator. During an ultrasound scan, the interventional tool isnavigated within the anatomical region relative to the acoustic imageplane, and the ultrasound transducers facilitate tracking by the tooltracker of a position of the interventional tool relative to theacoustic image plane. One or more aspects of a graphical icon aremodulated by the image navigator responsive to the tracked distance ofthe interventional tool relative to the acoustic image plane.

Document US20110282188A1 discloses a needle guidance system thatutilizes ultrasound imaging. In one embodiment, the guidance systemcomprises an imaging device including a probe for producing an image ofan internal body portion target. One or more sensors on the probe sensethe magnetic field of a magnet included with the needle. The systemincludes a display for depicting the position and/or orientation of theneedle together with the image of the target.

Document WO2014207666A1 discloses a system for tracking an instrumentwith ultrasound. The system includes a probe for transmitting andreceiving ultrasonic energy and a transducer associated with the probeand configured to move with the probe during use. A medical instrumentincludes a sensor configured to respond to the ultrasonic energyreceived from the probe. A control module is stored in memory andconfigured to interpret the ultrasonic energy received from the probeand the sensor to determine a three dimensional location of the medicalinstrument and to inject a signal to the probe from the transducer tohighlight a position of the sensor in an image.

Document US20100298704A1 discloses an ultrasound system that has anultrasound transducer equipped with a position marker and a needleequipped with a position marker. The position markers allow the positionand orientation of the transducer and needle to be determined. A displaydepicts an ultrasound image acquired via the transducer and a graphicalelement representative of a projection of the longitudinal axis of theneedle onto a plane of the ultrasound image.

A drawback of the above-mentioned systems arises from the fact that itis the position of the ultrasound detector that is determined andsubsequently displayed in the ultrasound image. Typically a user isinterested in the position of a particular functional part of theinstrument, such as the distal end of a needle, rather than the positonof the ultrasound detector itself However, the mechanical constraints ofsuch instruments hampers the ability to position the ultrasound detectorat-will, for example at the tip of a needle where it might interferewith insertion. Another drawback of known localization systems occursmore specifically when they are used in conjunction with a planarultrasound imaging system.

Owing to the separation between the ultrasound detector being trackedand the functional part on the instrument, the ultrasound detector maybe out-of-plane when the functional part is in-plane, but poorly visibleunder ultrasound. Thus it would be beneficial to indicate when afunctional part of the instrument, such as the tip of a needle, isin-plane.

SUMMARY OF THE INVENTION

In seeking to alleviate the drawbacks of known localization systems, anapparatus is provided for determining a position of an interventionaldevice respective an image plane of an ultrasound field defined by aplurality of beams emitted by an ultrasound transducer array of abeamforming ultrasound imaging system in which the position isdetermined based on ultrasound signals emitted by the ultrasoundtransducer array that have been detected by an ultrasound detectorattached to the interventional device. The apparatus includes an imagereconstruction unit, a position determination unit, a geometry-providingunit and an image fusion unit. The image reconstruction unit isconfigured to provide a reconstructed ultrasound image corresponding tothe image plane based on the ultrasound signals detected by theultrasound transducer array. The position determination unit isconfigured to identify, based on a correlation of the ultrasound signalsemitted by the ultrasound transducer array with the ultrasound signalsdetected by the ultrasound detector, the position of the interventionaldevice respective the image plane. Moreover the position of theinterventional device includes an out-of-plane distance corresponding tothe shortest distance between the ultrasound detector and the imageplane. The geometry-providing unit comprises a plurality oftransducer-to-distal-end lengths, wherein each length corresponds to apredetermined distance between a distal end of an interventional deviceand an ultrasound detector attached to the interventional device, foreach of a plurality of interventional device types. The image fusionunit is configured to i) receive data indicative of the type of theinterventional within the ultrasound field; and based on the type of theinterventional device to ii) select from the geometry-providing unit, acorresponding transducer-to-distal-end length; and to iii) indicate inthe reconstructed ultrasound image both the out-of-plane distance andthe transducer-to-distal-end length for the interventional device withinthe ultrasound field.

In so doing, an apparatus is provided which can be used to track theposition of an interventional device within an ultrasound field.Depending on the particular type of interventional device that is beingtracked, the geometry-providing unit selects the correspondingtransducer-to-distal-end length, and indicates this in the reconstructedimage in combination with the out-of-plane distance of the ultrasoundtransducer. Thus, the apparatus provides improved determination of theposition of the distal end of the interventional device. Moreover,because both the transducer-to-distal-end length and the out-of-planedistance are indicated in the reconstructed image, the position of thedistal end of the interventional device in relation to the image planeis more accurately determined.

In accordance with another aspect of the invention the image fusion unitis further configured to i) indicate the out-of-plane distance in thereconstructed ultrasound image as the radius of a first circle; and toii) indicate the transducer-to-tip length in the reconstructedultrasound image as the radius of a second circle. The first circle andthe second circle share a common centre, and the common centrecorresponds to the position of the ultrasound detector. In so doing thedetermination of the position of the distal end of the interventionaldevice respective the image plane of the beamforming ultrasound imagingsystem is improved because the first circle and the second circlecoincide when the tip of the interventional device is in-plane.

In accordance with another aspect of the invention an interventionaldevice that is adapted for use with the apparatus is described. Theinterventional device includes an ultrasound detector and a datacarrier. The ultrasound detector is adapted for detecting ultrasoundsignals emitted by an ultrasound transducer array of a beamformingultrasound imaging system. Moreover the ultrasound detector is attachedto the interventional device at a predetermined distance from a distalend of the interventional device. The data carrier comprises dataindicative of a type of the interventional device. Moreover, when thisdata, is received by the image fusion unit of the apparatus, the imagefusion unit is caused to: i) select from the geometry-providing unit ofthe apparatus, a transducer-to-distal-end length corresponding to thepredetermined distance between the distal end of the interventionaldevice and the ultrasound detector attached thereto, for theinterventional device type; and ii) to indicate in the reconstructedultrasound image that is reconstructed by the image reconstruction unitof the apparatus of claim 1 the transducer-to-distal-end length for theinterventional device within the ultrasound field.

In so doing the data stored in the data carrier of the interventionaldevice, when received by the apparatus, brings about the benefit ofimproved determination of the position of the distal end of theinterventional device respective the image plane of the beamformingultrasound imaging system.

In accordance with another aspect of the invention a computer programproduct is disclosed. The computer program product may be used inconjunction with the apparatus.

It is to be noted that the various aspects or embodiments described inrelation to the apparatus may also be used in combination or isolationwith aspects or embodiments of the interventional device, and likewisewith aspects and embodiments of the computer program product, and viceversa.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a beamforming ultrasound imaging system 15 incombination with an interventional device 11 and a first embodiment ofthe invention 10.

FIG. 2 illustrates an exemplary lookup table 23 that includes aplurality of transducer-to-distal-end lengths Ltde for each of aplurality of corresponding interventional device types T.

FIG. 3 illustrates a reconstructed ultrasound image RUI that includes aregion of interest ROI and in which both the out-of-plane distance Dopand the transducer-to-distal-end length Ltde are illustrated as circlesCop and Cde respectively.

FIG. 4 illustrates an intervention device 41 that is suitable for usewith the first embodiment of the invention.

FIG. 5 illustrates various method steps, or instructions that may becarried out in accordance with apparatus 10 of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

In order to illustrate the principles of the present invention, varioussystems are described in which the position of an interventional device,exemplified by a medical needle, is determined within the image plane ofan ultrasound field defined by the beams emitted by the linear array ofa 2D ultrasound imaging probe.

It is however to be appreciated that the invention also findsapplication in determining the positon of other interventional devicessuch as a catheter, a guidewire, a probe, an endoscope, an electrode, arobot, a filter device, a balloon device, a stent, a mitral clip, a leftatrial appendage closure device, an aortic valve, a pacemaker, anintravenous line, a drainage line, a surgical tool such as a tissuesealing device or a tissue cutting device.

It is also to be appreciated that the invention finds application inbeamforming ultrasound imaging systems having other types of imagingprobes and other types of ultrasound arrays which are arranged toprovide a planar image, such as the 2D array of a 3D imaging probe, a“TRUS” transrectal ultrasonography probe, an “IVUS” intravascularultrasound probe, a “TEE” transesophageal probe, a “TTE” transthoracicprobe, a “TNE” transnasal probe, an “ICE” intracardiac probe.

FIG. 1 illustrates a beamforming ultrasound imaging system 15 incombination with an interventional device 11 and a first embodiment ofthe invention 10. In FIG. 1, beamforming ultrasound imaging system 15includes a 2D ultrasound imaging probe 18 which is in communication withimage reconstruction unit IRU, imaging system processor ISP, imagingsystem interface ISI and display DISP. The units IRU, ISP, ISI and DISPare conventionally located in a console with which 2D ultrasound imagingprobe 18 is in wired communication. It is also contemplated thatwireless communication, for example using an optical, infrared, or an RFcommunication link, may replace the wired link. It is also contemplatedthat some of units IRU, ISP, ISI and DISP may alternatively be locatedwithin 2D ultrasound imaging probe 76, as is the case for example in thePhilips VISIQ ultrasound imaging system. In FIG. 1, 2D imaging probe 18includes linear ultrasound transducer array 14 that transmits andreceives ultrasound energy within an ultrasound field that interceptsvolume of interest VOI. The ultrasound field is fan-shaped in FIG. 1 andincludes multiple ultrasound beams B_(1 . . . k) that define an imageplane 12. Beamforming ultrasound imaging system 15 may also includeelectronic driver and receiver circuitry (not shown) that is configuredto amplify and/or to adjust the phase of signals transmitted by orreceived by 2D ultrasound imaging probe 18 in order to generate anddetect the ultrasound signals in beams B_(1 . . . k). The electronicdriver and receiver circuitry may thus be used to steer the emittedand/or received ultrasound beam direction.

In-use, the beamforming ultrasound imaging system 15 is operated in thefollowing way. An operator may plan an ultrasound procedure via imagingsystem interface ISI. Once an operating procedure is selected, imagingsystem interface ISI triggers imaging system processor ISP to executeapplication-specific programs that generate and interpret the signalstransmitted to and detected by 2D ultrasound imaging probe 18.Beamforming ultrasound imaging system 15 may also include a memory (notshown) for storing such programs. The memory may for example storeultrasound beam control software that is configured to control thesequence of ultrasound signals transmitted by and/or received by imagingprobe 18. Image reconstruction unit IRU, which may alternatively formpart of imaging system processor ISP, reconstructs data received fromthe imaging probe 18 into an image corresponding to image plane 12 andwhich thus intercepts volume of interest VOI, and subsequently displaysthis image via display DISP. The reconstructed image may for example bean ultrasound Brightness-mode “B-mode” image, otherwise known as a “2Dmode” image, a “C-mode” image or a Doppler mode image, or indeed anyultrasound planar image.

Also shown in FIG. 1 is an interventional device 11 and a firstembodiment of the invention 10 that may be used to track the position ofinterventional device 11 respective image plane 12 of beamformingultrasound imaging system 15. The first embodiment of the invention 10includes image reconstruction unit IRU, position determination unit PDU,geometry providing unit GPU, and image fusion unit IFU, each of theseunits being in communication with one another as illustrated by theinterconnecting arrows. Interventional device 11 that is to be tracked,includes an ultrasound detector 16 that is positioned at a predetermineddistance Ltde from distal end 17 of interventional device 11.

In-use, the position of interventional device 11, or more specificallythat of ultrasound detector 16 attached thereto, is tracked respectiveimage plane 12 by position determination unit PDU based on theultrasound signals corresponding to its beams B_(1 . . . k) that havebeen detected by ultrasound transducer 16. Position determination unitPDU identifies the position of ultrasound detector 16 based on acorrelation of the ultrasound signals emitted by the ultrasoundtransducer array with the ultrasound signals detected by the ultrasounddetector. More specifically this correlation may be based on i) the timedelay between emission of each beam B_(1 . . . k) and its detection byultrasound detector 16, and ii) based on the amplitude of the ultrasoundsignals corresponding to each beam detected by the ultrasound detector.In more detail, the correlation essentially determines the ultrasounddetector 16 position that, based on the emitted sequence of ultrasoundsignals, most closely matches the detected ultrasound signals. This maybe illustrated as follows. When the ultrasound detector 16 is in thevicinity of image plane 12, ultrasound signals from the nearest of beamsB_(1 . . . k) to the detector will be detected with a large amplitudewhereas more distant beams will be detected with relatively smalleramplitudes. This amplitude can be modeled to vary in dependence on therange between the emitter and the detector, and the out-of-planedistance Dop between the detector 16 and the image plane 12. Moreoverthe time delay between emission and detection of the beam depends uponthe range between the emitter and the detector for each emitted beam.The range is determined by multiplying the time delay by the speed ofultrasound propagation. The correlation between the ultrasound signalsemitted by the ultrasound transducer array with the ultrasound signalsdetected by the ultrasound detector determines the best fit position ofultrasound detector 16 respective image plane 12. The out-of-planedistance may also be obtained by triangulating the position of thedetector respective the ultrasound image plane.

The geometry-providing unit GPU of the first embodiment includes aplurality of transducer-to-distal-end lengths. Moreover, each lengthcorresponds to a predetermined distance between a distal end of aninterventional device and an ultrasound detector attached to theinterventional device, for each of a plurality of interventional devicetypes. The geometry-providing unit GPU may, for example, be provided bya lookup table. FIG. 2 illustrates an exemplary lookup table 23 thatincludes a plurality of transducer-to-distal-end lengths Ltde for eachof a plurality of corresponding interventional device types T. Lookuptable 23 in FIG. 2 may be used in the geometry-providing unit GPU ofFIG. 1. In FIG. 1, type T₁ may for example correspond to a vascularaccess needle having an ultrasound transducer positioned 5.0 mm from itsdistal end, type T₂ may for example be a catheter, and exemplaryinterventional device type T₃ may be a tissue sealing tool. Other typesof interventional device may be included in the lookup table in the sameway.

The image fusion unit IFU of the first embodiment is arranged to receivedata indicative of the type T of the interventional device within theultrasound field. Moreover, based on the type T of the interventionaldevice, the image fusion unit IFU selects from the above-describedgeometry-providing unit GPU, a corresponding transducer-to-distal-endlength Ltde; and indicates in the reconstructed ultrasound image that isreconstructed by the image reconstruction unit IRU, both theout-of-plane distance Dop and the transducer-to-distal-end length Ltdefor the interventional device within the ultrasound field. Since boththe out-of-plane distance Dop and the transducer-to-distal-end lengthLtde are indicated in the reconstructed image by image fusion unit IFU,it is immediately apparent when the distal end of the interventionaldevice is in image plane 12. Moreover, the image fusion unit IFU thatautomatically selects the corresponding transducer-to-distal-end lengthLtde from the geometry-providing unit GPU allows the tracking system tooperate with different types of interventional device, and to correctlyindicate their geometry in the reconstructed ultrasound image.

Each of the units: image fusion unit IFU, geometry-providing unit GPU,position determination unit PDU, and image reconstruction unit IRU maybe provided by one or more processors including instructions to performits respective function. Moreover, one or more of these units may beprovided by imaging system processor ISP of beamforming ultrasoundimaging system 15.

In one implementation the type T of the interventional device may bereceived by image fusion unit IFU wirelessly from a data carrierassociated with the interventional device. In this example the datacarrier may be, for example, an RFID chip, or a barcode or a QR code. Inanother example the data may be received via wired communication withthe data carrier, for example from a memory associated with theinterventional device. Thus the data carrier may be, for example, anRFID chip, or a barcode such as a linear or matrix barcode or a QR code,a memory or indeed any machine-readable data carrier. The image fusionunit may thus include a reader such as a barcode reader, an RFID reader,or a data reader for reading a memory, for reading the data in the datacarrier. Alternatively a user may input this data manually to the imagefusion unit.

The out-of-plane distance Dop and the transducer-to-distal-end lengthLdte may be indicated in the reconstructed ultrasound image by variousmeans, including in the form of a numerical indicator, a dial, or as ashape having a size that corresponds to the respective distance, orlength. This may be provided for example as an overlay image on thereconstructed image, i.e. by fusing data from the indicator with theultrasound image. Various colors may also be used to provide the desiredindication. In a preferred example that is illustrated in FIG. 3,circles are used as the indicators. FIG. 3 illustrates a reconstructedultrasound image RUI that includes a region of interest ROI and in whichboth the out-of-plane distance Dop and the transducer-to-distal-endlength Ltde are illustrated as circles Cop and Cde respectively. In thisexample, the image fusion unit IFU is arranged to indicate theout-of-plane distance in the reconstructed ultrasound image as theradius of a first circle Cop; and to indicate the transducer-to-tiplength in the reconstructed ultrasound image as the radius of a secondcircle Cde. Moreover the first circle and the second circle share acommon centre, and the common centre corresponds to the position of theultrasound detector. In FIG. 3A the tip of the interventional device issomewhat out-of-plane, and Dop>Ltde, as indicated by the radius ofcircle of Cop exceeding that of Cde. As the tip of the interventionaldevice is advanced towards the image plane the difference between theradii of the circles Cop and Cde decreases, as illustrated in FIG. 3B.When the tip of the interventional device is in-plane the radii of thecircles Cop and Cde are the same and the perimeters of the circlescoincide. In this way, a user is assisted in determining the position ofthe tip of the interventional device respective the ultrasound imageplane. As to the actual position of the tip of the interventional deviceon the image plane, the common centre of the two circles is located atthe closest point to the position of the ultrasound detector. Howeverthe exact position of the tip of the interventional device depends onthe angle of a line between the interventional device tip and theultrasound detector, respective the image plane. In conventional use ofthe interventional device with the beamforming ultrasound imagingsystem, this line is typically close to perpendicular to the image planeand thus the tip will lie at the common centre of the circles.Confirmation of this perpendicular arrangement is provided to a userduring insertion of the interventional device in the region of interestROI because in this arrangement the common centre remains in a fixedposition respective on the image plane during insertion. As this linedeviates from a perpendicular position the position of the tip in theultrasound image is moved away from the common centre, but is alwayswithin the circle Cde. When the interventional device is inserted into aregion of interest, intermittent images of the tip of the interventionaldevice as provided by the beamforming ultrasound imaging system, and thedisplacement of parts of the region of interest, also confirm theindications provided by the circles.

Optionally, the image fusion unit may be further configured such thatwhen the perimeter of the first circle and the perimeter of the secondcircle coincide, the first circle and the second circle are indicated asa common circle and at least one of the following occurs i) theperimeter of the common circle is indicated in a color that differs fromthe color of the first circle and from the color of the second circle;ii) the perimeter of the common circle is indicated with a contrast thatdiffers from the contrast of the first circle and from the contrast ofthe second circle; iii) the common circle is displayed with a dashedperimeter; iv) the perimeter of the common circle is configured to pulseover time. These indications in the common circle alert to a user thatthe tip of the interventional device is in-plane respective the imageplane of the ultrasound imaging system.

FIG. 4 illustrates an intervention device 41 that is suitable for usewith the first embodiment of the invention. The interventional deviceincludes an ultrasound detector 46 and a data carrier 49. The ultrasounddetector is adapted for detecting ultrasound signals emitted by anultrasound transducer array of a beamforming ultrasound imaging system.Ultrasound detector 46 is attached to interventional device 41 at apredetermined distance Ltde from a distal end 47 of interventionaldevice 41. Data carrier 49 includes data indicative of a type T ofinterventional device 41. Moreover, this data, when received by theimage fusion unit IFU of the first embodiment of the invention, causesimage fusion unit IFU to i) select from the geometry-providing unit GPUof the first embodiment of the invention, a transducer-to-distal-endlength Ltde corresponding to the predetermined distance between thedistal end 47 of the interventional device 41 and the ultrasounddetector 46 attached thereto, for the interventional device type T; andto ii) indicate in the reconstructed ultrasound image RUI that isreconstructed by the image reconstruction unit IRU of the firstembodiment of the invention the transducer-to-distal-end length Ltde forthe interventional device within the ultrasound field.

In FIG. 4, data carrier 49 may for example be a barcode such as a linearor matrix barcode or a QR code, an RFID chip, a memory, or indeed anymachine-readable data carrier. The data carrier may be attached to theinterventional device by various known means including adhesives, or itmay be applied by printing, etching, and the like. Also, whilstillustrated as being disposed on the interventional device 41, datacarrier 49 may alternatively be positioned on the packaging ofinterventional device 41, for example for sterility reasons.

Thus, when the interventional device of FIG. 4 is used with the firstembodiment of the invention, i.e. item 10 in FIG. 1, the data receivedby the image fusion unit IFU enables the technical effect of improveddetermination of the position of the interventional device respectivethe image plane of the beamforming ultrasound imaging system.

Optionally the data carrier's data, when received by the image fusionunit IFU of FIG. 1 further causes the image fusion unit to indicate thetransducer-to-tip length in the reconstructed ultrasound image as theradius of a second circle; i.e. Cde in FIG. 3.

Optionally the data carrier's data, when received by the image fusionunit IFU of FIG. 1 further causes the image fusion unit to indicate inthe reconstructed ultrasound image, an out-of-plane distance Dopcorresponding to the shortest distance between the ultrasound detectorand the image plane, as determined by the position determination unitPDU of the first embodiment of the invention.

Optionally the data carrier's data, when received by the image fusionunit IFU of FIG. 1 further causes the image fusion unit to indicate theout-of-plane distance Dop in the reconstructed ultrasound image RUI asthe radius of a first circle Cop; wherein the first circle Cop and thesecond circle Cde share a common centre, and wherein the common centrecorresponds to the position of the ultrasound detector.

Advantageously these additional effects that are triggered in the imagefusion unit IFU bring about improved accuracy of determination of theposition of the interventional device respective the image plane of thebeamforming ultrasound imaging system.

Whilst the exemplary interventional device illustrated in FIG. 1 andFIG. 4 is a needle, other types of interventional device may be trackedin the same way with the above-described ultrasound detector, such as acatheter, a guidewire, a probe, an endoscope, an electrode, a robot, afilter device, a balloon device, a stent, a mitral clip, a left atrialappendage closure device, an aortic valve, a pacemaker, an intravenousline, a drainage line, a surgical tool such as a tissue sealing deviceor a tissue cutting device.

The ultrasound detector 46 illustrated in FIG. 1 and FIG. 4 may beprovided by a number of piezoelectric materials, both hard and softpiezoelectric materials being suitable.

Preferably ultrasound detector 46 is formed from Polyvinylidenefluoride, otherwise known as PVDF whose mechanical properties andmanufacturing processes lend themselves to attachment to curved surfacessuch as needles. Alternative materials include a PVDF co-polymer such aspolyvinylidene fluoride trifluoroethylene, a PVDF ter-polymer such asP(VDF-TrFE-CTFE). Preferably the ultrasound detector is wrapped aroundan axis of the interventional device in order to provide sensing around360 degrees of rotation about the axis although this need not always bethe case. Moreover, the ultrasound detector may include various wires ora wireless communication module that are not shown in FIG. 4 forcommunicating detected ultrasound signals with the positiondetermination unit PDU in FIG. 1. Preferably there is a single, i.e. oneand only one, such ultrasound detector disposed on the interventionaldevice. Advantageously this simplifies the form factor of theinterventional device, any electrical interconnect that may be present,and the processing of any detected ultrasound signals. Alternatively,two or more ultrasound detectors may be used to provide positionredundancy, and/or an indication of the trajectory of the interventionaldevice.

FIG. 5 illustrates various method steps, or instructions that may becarried out in accordance with apparatus 10 of FIG. 1. The instructionsmay be stored on a computer program product and may be executed by ormore processors. The method steps include: i) reconstructing, RECON, anultrasound image corresponding to the image plane based on theultrasound signals detected by the ultrasound transducer array; ii)identifying, IDEN, based on a correlation of the ultrasound signalsemitted by the ultrasound transducer array with the ultrasound signalsdetected by the ultrasound detector, and optionally based on the timedelay between emission of each beam and its detection by the ultrasounddetector, and optionally based on the amplitude of the ultrasoundsignals corresponding to each beam detected by the ultrasound detector,the position of the interventional device respective the image plane;and wherein the position of the interventional device includes anout-of-plane distance corresponding to the shortest distance between theultrasound detector and the image plane; iii) receiving data, RECD,indicative of a type of the interventional device within the ultrasoundfield; and based on the type of the interventional device: iv)selecting, SEL, from a lookup table, a transducer-to-distal-end lengththat corresponds to a predetermined distance between a distal end of theinterventional device and the ultrasound detector attached to theinterventional device; and v) indicating, INDIC, in the reconstructedultrasound image, both the out-of-plane distance and thetransducer-to-distal-end length for the interventional device within theultrasound field. The instructions may also include one or moreadditional steps described herein in relation to FIG. 1.

The computer program product may be provided by dedicated hardware, orhardware capable of executing software in association with appropriatesoftware. When provided by a processor, the functions can be provided bya single dedicated processor, by a single shared processor, or by aplurality of individual processors, some of which can be shared.Moreover, explicit use of the term “processor” or “controller” shouldnot be construed to refer exclusively to hardware capable of executingsoftware, and can implicitly include, without limitation, digital signalprocessor “DSP” hardware, read only memory “ROM” for storing software,random access memory “RAM”, non-volatile storage, etc. Furthermore,embodiments of the present invention can take the form of a computerprogram product accessible from a computer-usable or computer-readablestorage medium providing program code for use by or in connection with acomputer or any instruction execution system. For the purposes of thisdescription, a computer-usable or computer readable storage medium canbe any apparatus that may include, store, communicate, propagate, ortransport the program for use by or in connection with the instructionexecution system, apparatus, or device. The medium can be an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,or apparatus or device, or a propagation medium. Examples of acomputer-readable medium include a semiconductor or solid state memory,magnetic tape, a removable computer diskette, a random access memory“RAM”, a read-only memory “ROM”, a rigid magnetic disk and an opticaldisk. Current examples of optical disks include compact disk-read onlymemory “CD-ROM”, compact disk-read/write “CD-R/W”, Blu-Ray™ and DVD.

In the above first, preferred embodiment described above in relation toFIG. 1-4 the data carrier of the interventional device includes dataindicative of the needle type. In a second embodiment the data carriermay additionally or alternatively include data indicative of thetransducer-to-distal-end length Ltde corresponding to the predetermineddistance between the distal end of the interventional device and theultrasound detector attached thereto. In this second embodiment thegeometry-providing unit may thus be omitted from FIG. 1. Moreover theimage fusion unit IFU of FIG. 1 may instead be configured to receivedata indicative of the transducer-to-distal-end length Ltde of theinterventional device; and to indicate in the reconstructed ultrasoundimage both the out-of-plane distance Dop and thetransducer-to-distal-end length Ltde. In other words, in thisembodiment, the type of the needle may no longer be used in the lookupprocess and the data carrier stores the distance between the distal endof the interventional device and the ultrasound detector attachedthereto.

In a third embodiment of the invention, which may be used in combinationwith either the first or the second embodiments, or as an alternativethereto, the data carrier may include a data field indicative of one ormore of the following: a length of the ultrasound detector along an axisextending between the ultrasound transducer and the distal end of theinterventional device; a width of the ultrasound detector perpendicularto an axis extending between the ultrasound transducer and the distalend of the interventional device. Such data may also be indicated in thereconstructed image by the image fusion unit IFU. The respectiveparameter may for example be indicated in the form of the thickness ofthe perimeter of the first circle Cop or of the second circle Cde, or bythird circle having a radius that corresponds to the extent of theultrasound transducer and which shares a common centre with the secondcircle Cde. In this way perimeter thickness, or the extent of the thirdcircle is indicative of the uncertainty of the position of theinterventional device arising from the ultrasound detector's finitelength and width. Either of these data fields may be stored on the datacarrier and thus received therefrom by the image fusion unit IFU, orassociated with the interventional device Type and stored in a lookuptable similar to that of FIG. 2 and thus received by the image fusionunit IFU from the geometry providing unit GPU.

1. Apparatus for determining a position of an interventional devicerespective an image plane of an ultrasound field defined by a pluralityof beams (B_(1 . . . k)) emitted by an ultrasound transducer array of abeamforming ultrasound imaging system in which the position isdetermined based on ultrasound signals emitted by the ultrasoundtransducer array that have been detected by an ultrasound detectorattached to the interventional device; the apparatus comprising: animage reconstruction unit (IRU) configured to provide a reconstructedultrasound image (RUI) corresponding to the image plane based on theultrasound signals detected by the ultrasound transducer array; and aposition determination unit (PDU) configured to identify, based on acorrelation of the ultrasound signals emitted by the ultrasoundtransducer array with the ultrasound signals detected by the ultrasounddetector, the position of the interventional device respective the imageplane; and wherein the position includes an out-of-plane distance (Dop)corresponding to the shortest distance between the ultrasound detectorand the image plane; and a geometry-providing unit (GPU) comprising aplurality of transducer-to-distal-end lengths (Ltde_(1 . . . n)) whereineach length corresponds to a predetermined distance (Ltde) between adistal end of an interventional device and an ultrasound detectorattached to the interventional device, for each of a plurality ofinterventional device types (T_(1 . . . n)); and an image fusion unit(IFU) configured to: receive data indicative of the type (T) of theinterventional device within the ultrasound field; and based on the type(T) to: select from the geometry-providing unit (GPU), a correspondingtransducer-to-distal-end length (Ltde); and to indicate in thereconstructed ultrasound image (RUI) both the out-of-plane distance(Dop) and the transducer-to-distal-end length (Ltde) for theinterventional device within the ultrasound field wherein theout-of-plane distance (Dop) is indicated in the reconstructed ultrasoundimage (RUI) as the size of a first shape (Cop); and wherein thetransducer-to-tip length (Ltde) is indicated in the reconstructedultrasound image (RUI) as the size of a second shape (Cde); and whereinthe first shape (Cop) and the second shape (Cde) share a common centre,and wherein the common centre corresponds to the position of theultrasound detector.
 2. The apparatus of claim 1 wherein: the size ofthe first shape is the radius of a first circle (Cop); and to whereinthe size of the second shape is the radius of a second circle (Cde). 3.The apparatus of claim 2 wherein the common centre is located in theimage plane at the closest point to the position of the ultrasounddetector.
 4. The apparatus of claim 2 wherein the image fusion unit(IFU) is further configured such that when the perimeter of the firstcircle (Cop) and the perimeter of the second circle (Cde) coincide, thefirst circle and the second circle are indicated as a common circle andat least one of the following occurs: the perimeter of the common circleis indicated in a color that differs from the color of the first circleand from the color of the second circle; the perimeter of the commoncircle is indicated with a contrast that differs from the contrast ofthe first circle and from the contrast of the second circle; the commoncircle is displayed with a dashed perimeter; the perimeter of the commoncircle is configured to pulse over time.
 5. The apparatus of claim 1further comprising an ultrasound transducer array.
 6. The apparatus ofclaim 1 further comprising an interventional device having an ultrasounddetector attached thereto; wherein the ultrasound detector is attachedto the interventional device at a predetermined distance (Ltde) from adistal end of the interventional device.
 7. The apparatus of claim 1wherein the beamforming ultrasound imaging system comprises an imagingprobe selected from the group: a 2D ultrasound imaging probe, a 3Dultrasound imaging probe, a transrectal ultrasonography probe, anintravascular ultrasound probe, a transesophageal probe, a transthoracicprobe, a transnasal probe, an intracardiac probe.
 8. The apparatus ofclaim 1 further comprising an interventional device wherein saidinterventional device comprises: an ultrasound detector for detectingultrasound signals emitted by an ultrasound transducer array of abeamforming ultrasound imaging system; and a data carrier; wherein theultrasound detector is attached to the interventional device at apredetermined distance (Ltde) from a distal end of the interventionaldevice; and wherein the data carrier comprises data indicative of a type(T) of the interventional device, and the data, when received by theimage fusion unit (IFU) of the apparatus, causes the image fusion unit(IFU) to: select from the geometry-providing unit (GPU) of theapparatus, the transducer-to-distal-end length (Ltde) corresponding tothe predetermined distance between the distal end of the interventionaldevice and the ultrasound detector attached thereto, for theinterventional device type (T); and to indicate in the reconstructedultrasound image (RUI) that is reconstructed by the image reconstructionunit (IRU) of the apparatus the transducer-to-distal-end length (Ltde)for the interventional device within the ultrasound field.
 9. Theinterventional device of claim 8 wherein the ultrasound detector isformed from a piezoelectric material, for example Polyvinylidenefluoride, a PVDF co-polymer such as polyvinylidene fluoridetrifluoroethylene, a PVDF ter-polymer such as P(VDF-TrFE-CTFE).
 10. Theinterventional device of claim wherein the interventional device isselected from the group: a needle, a catheter, a guidewire, a probe, anendoscope, an electrode, a robot, a filter device, a balloon device, astent, a mitral clip, a left atrial appendage closure device, an aorticvalve, a pacemaker, an intravenous line, a drainage line, a surgicaltool such as a tissue sealing device or a tissue cutting device. 11.Computer program product comprising instructions which when executed ona processor of an apparatus for determining a position of aninterventional device respective an image plane of an ultrasound fielddefined by a plurality of beams (B_(1 . . . k)) emitted by an ultrasoundtransducer array of a beamforming ultrasound imaging system in which theposition is determined based on ultrasound signals emitted by theultrasound transducer array that have been detected by an ultrasounddetector attached to the interventional device, cause the processor tocarry out the method steps of: reconstructing an ultrasound image (RUI)corresponding to the image plane based on the ultrasound signalsdetected by the ultrasound transducer array; identifying, based on acorrelation of the ultrasound signals emitted by the ultrasoundtransducer array with the ultrasound signals detected by the ultrasounddetector, the position of the interventional device respective the imageplane; and wherein the position includes an out-of-plane distance (Dop)corresponding to the shortest distance between the ultrasound detectorand the image plane; receiving data indicative of a type (T) of theinterventional device within the ultrasound field; and based on the type(T): selecting, from a lookup table, a transducer-to-distal-end lengththat corresponds to a predetermined distance (Ltde) between a distal endof the interventional device and the ultrasound detector attached to theinterventional device; indicating, in the reconstructed ultrasound image(RUI), both the out-of-plane distance (Dop) and thetransducer-to-distal-end length (Ltde) for the interventional devicewithin the ultrasound field; wherein the out-of-plane distance (Dop) isindicated in the reconstructed ultrasound image (RUI) as the size of afirst shape (Cop); and wherein the transducer-to-tip length (Ltde) isindicated in the reconstructed ultrasound image (RUI) as the size of asecond shape (Cde); and wherein the first shape (Cop) and the secondshape (Cde) share a common centre, and wherein the common centrecorresponds to the position of the ultrasound detector.
 12. Computerprogram product of claim 13 wherein the size of the first shape is theradius of a first circle (Cop); and wherein the size of the second shapeis the radius of a second circle (Cde),